Electronic ignition system

ABSTRACT

An electrical control system for turning on a solenoid valve to supply fuel to a burner, and wherein the valve remains on only if ignition of fuel occurs within a predetermined time as a consequence of a cojointly controlled igniting spark device. The system energizes a circuit for generating high voltage sparking potential and automatically drops out the circuit when ignition occurs or fails to occur within a predetermined time. The system is particularly adapted for use with a direct current source of limited energy storage capacity and includes features which minimize power consumption during operation.

United States Patent [191 McKenn'a [111 3,820,939 [451 June 28, 1974 1 1 ELECTRONIC, IGNITION SYSTEM [75] Inventor: William F. McKenna, Rockford, 111. [73] Assignee: Atwood Vacuum Machine Company,

Primary ExaminerEdward G. Favors I Attorney, Agent, or Firm-Wolf, Hubbard, Leydig, Voit & Osann, Ltd.

[ 5 7 ABSTRACT An electrical control system for turning on a solenoid valve to supply fuel to a burner. and wherein the valve remains on only if ignition of fuel occurs within a predetermined time as a consequence of a cojointly controlled igniting spark device. The system energizes a circuit for generating high voltage sparking potential and automatically drops out the circuit when ignition occurs or fails to occur within a predetermined time. The system is particularly adapted for use with a direct current source of limited energy storage capacity and includes features which minimize power consumption during operation.

13 Claims, 2 Drawing Figures PATENIED Jllll 28 I974 sum 1 or 2 /T\\\\ a W SHEET 2 0F 2 PATENTEBmza m4 1 i ELECTRONIC IGNITION SYSTEM BACKGROUND OF THE INVENTION The present invention generally relates to an electrical system for controlling a utilization device and a coacting enabling device; and, more particularly, to an electrical ignition control system for use with oil or gas burning appliances.

The recent flurry of commercial activity in the leisure and recreational area has resulted in many new products, particularly with respect to camping trailers, selfpropelled campers and the like. These vehicles and trailers are often equipped with space heating units as well as water heaters which, of course, must be ignited. Although oil or gas heating units, for example, may be manually ignited by turning on a fuel line and lighting the burner, it is desirable to have an automatic ignition system, since many people find it undesirable to manually ignite such burners, probably because they are somewhat fearful of the remote possibility of an oil or gas explosion. Moreover, in the event the flame goes out when the valve is open, the oil or gas will continue to flow from the supply and can easily create a dangerous explosive situation. Automatic ignition and shut down in response to closure or opening of thermostatic switch contacts is the arrangement preferred by users.

While automatic ignition systems for oil and gas burners are presently available, they often require an alternating current source, i.e., either an ac. generator or an external ac. source which may be unavailable in many locations. Since a system for igniting oilor gas burners in a camping trailer or the like most conveniently only has a power source consisting of a battery supplying a dc. voltage, it is important for the ignition system to consume as little power as possible from the source during operation. This is particularly true if the system is intended to control the ignition of a water heater, space heater or the like having thermostatic control wherein flame ignition and termination thereof may occur quite frequently.

. It is one aim of the present invention to providea control system for a utilization device such as a solenoid valve or the like wherein the system is adapted for use with a limited dc. voltage supply and which will not consume substantial amounts of energy during operation.

Another object of the present invention is to provide a control system for a utilization device, such as a fuel supply solenoid valve, with greatly enhanced safety.

More specifically, it is an object to provide controls which prohibit a utilization device from being initially turned on if certain electrical components required for enabling functions (sparking for ignition) fail, and which also prohibit the device from remaining on if a predetermined response is not received within a specified time period, e.g., an ignition attempt is unsuccessful.

It is also an object of the present invention to provide an electronic control system for use in conjunction with circuitry that provides high voltage sparking for igniting an oil or gas burner and wherein the sparking will be promptly terminated if ignition is either successful or within a predetermined time period if ignition is unsuccessful. If the ignition trial is unsuccessful within the predetermined time, the utilization device controlling 2 the flow of fuel to the burner will also be automatically shut off.

Still another specific object of the present invention lies in the provision for requiring a higher voltage to initially turn on the utilization device and a lower sustaining voltage to maintain the utilization device turned on, the lower sustaining voltage beingeffective to reduce the level of power consumption from the source during operation.

Still another object of the present invention is to provide an electronic control circuit which is adapted to independently control two or more utilization devices while using certain common portions of the circuitry in the control of both devices and thereby reduce the system cost.

Still another specific object of the present invention is to provide an electronic control system for turning on a utilization device which includes an amplifying semiconductor device having emitter-base and emittercollector current paths and a capacitor connected in series with the emitter-base current path so that timing is done by the capacitor charged through the base circuit. This enables the use of a relatively small capacitor in conjunction with the relatively small base current to produce a relatively large time constant and the use of the collector current of the same device to turn on another device only during the period in whichthe capacitor is charging.

Other objects and advantages will become apparent upon reading the following detailed description, while referring to the attached drawings, in which:

FIG. 1 is a schematic diagram of the electrical control system embodying the present invention; and

FIG. 2 is an electrical schematic diagram illustrating a modification of the control system shown in FIG. 1.

While the invention will be hereinafter described in detail with reference to specific illustrated embodiments, it should be understood that it is not intended to limit the invention to such specific embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as may fall within the spirit and scope of the invention as defined in the appended claims. I

Turning now to the drawings and particularly FIG. 1, control circuitry embodying the present invention is shown in conjunction with a pair of high voltage electrodes 10 and 12 which together define a spark gap that is positioned adjacent a gas or oil burner 14 connected toa fuel supply (not shown) through a fuel line 16 and utilization device shown to be a solenoid valve 18. The burner 14 may be part of a space heater or water heater or the like and is adapted to be ignited once the valve 18 is opened and sparks are produced in the gap between the electrodes 10 and 12.

' Broadly stated, the control system of the present invention includes a spark generator circuit, indicated generally at 20, an oscillator, indicated generally at 22,

and timing, safety and monitoring circuits which make up the bulk of the remainder of the schematic diagram and which will be hereinafter described in detail. Since the embodiment here shown is particularly adapted for use in heating systems for trailers, campers and the like, which may not have a source of alternating current, a direct current dc.) source 24 is provided and is preferably a conventional 6 volt battery. The source voltage is applied to the circuitry through a main power switch 26, and assuming for example that a space heater is being controlled, through a thermostat 28, or the like.

To produce the spark between the electrodes and 12 required for flame ignition at the burner 14, the oscillator 22 converts the low dc. battery potential to a high voltage ac. signal, for example, 150 vac, which is required by the spark generating circuit 20. The oscillator 22 comprises transistors 34 and 36 having their respective collectors connected to the opposite bases through resistors 38 and 40 and their emitters connected together by a line 42. The collectors of the transistors 34, 36 are returned to the positive supply potential through respective primary windings 44 and 46 of a transformer 48. Assuming that line 42 is at ground potential and the switch 26 and the thermostat 28 are closed,'the source voltage will be applied through a diode 50 to a point 52 between the transformer primaries 44 and 46. Assuming transistor 34 to be initially conducting, the source current will flow into the transformer terminal 52, through the primary winding 44 and into the collector of transistor 34. This current flow induces a voltage across the primary winding 46 which drives the base of transistor 34 positive relative to its emitter, thereby enhancing conduction of transistor 34. With transistor 34 saturated, the base of transistor 36 is pulled down almost to ground potential, so transistor 36 is cut off. As the current increases the transformer 48 saturates, causing the induced voltage to drop to zero. The loss in induced voltage then causes the magnetic field in the transformer to collapse inducing a voltage of opposite polarity in the primary windings 44 and 46 which results in shutting off transistor 34 and turning on transistor 36. The switching action creates alternate periods of conduction through the primary windings 44, 46 and thus induces an ac. voltage in a secondary winding 54 of the transformer 48 which is selected so that the secondary voltage is preferably about 150 volts in amplitude.

To produce arcing or sparking between the gap electrodes 10 and 12, the high voltage ac. from the secondary winding 54 is rectified and caused to charge a capacitor which is periodically discharged through the primary winding 62 of a high voltage step-up transformer 64 having its secondary winding 67 in series with the spark gap. For this purpose, the ac. voltage is rectified by a diode 56 which conducts current unidirectionally through the winding 62 to charge a capacitor 68. This charging current is sufficiently small that it does not induce a voltage in the secondary winding 67 to cause arcing across the gap 10, 12. But the voltage built up across the capacitor 68 is applied through the winding 62 across a gas-filled diode discharge device 58 in series with a resistor 66. When that voltage reaches the break-down potential of the gas diode 58, a positive voltage drop across resistor 66 is applied between the gate g and cathode c of a silicon controlled rectifier (SCR) 60 having its anode-cathode path in series with the winding 62 and capacitor 68. Firing of the SCR permits the built-up charge on the capacitor to discharge suddenly through the winding 62 and the anode-cathode path, with the result that a very high voltage of short duration is induced in the secondary 67. A spark or arc discharge therefore is produced across the gap between electrodes 10, 12. The sparking will continue periodically as the capacitor 68 charges relatively slowly and is discharged suddenly and the are will serve to ignite any ccombustible gas or vapor at the burner 14.

In accordance with an important aspect of the present invention, provision is made to actuate a utilization device (here the valve 18) only if an enabling device (here the spark gap l2, l4 and its circuits 20, 22) are excited and operative-so that fuel flow is precluded unless ignition can occur and does in fact occur. More specifically, the control system of the present invention includes timing, safety and monitoring circuitry for selectively controlling the operation of the oscillator and spark generating circuitry as well as the utilization device shown to be a solenoid valve 18, so that fuel will not be transmitted to the burner 14 if ignition is not successful within a predetermined time. Additionally, it is effective to shut off the oscillator if ignition is successful, since continued sparking is unnecessary if ignition occurs and would merely result in excessive undesirable power consumption from the dc. power source 24.

To control the energization of the oscillator 22 and assuming the switch 26 and the thermostat 28 are closed, voltage from the source 24 is applied to a diode 72, the cathode of which is connected through solenoid coil 18a to the emitter of an amplifying semi-conductor device, which is shown to be a transistor 76. The collector of the transistor 76 is connected through a diode 80 to the base of a switching device, which is shown to be a transistor 78 although a relay or the like may be used. Additionally, the base of the transistor 76 is connected through a diode 82 to a parallel connected capacitor 84 and resistor 86 which lead to ground. The transistor 78 has its collector connected to line 42 of the oscillator and its emitter connected to ground, so that when the thermostat 28 closes (and thus applies the positive source voltage through the diode 50 to the transformer 48) current flows through diode 72, coil 18a, emitter and base of transistor 76, diode 82 and into capacitor 84 to charge the latter. Such emitter-base current turns on current flow through the emitter-collector path of transistor 76, and thus through the base-emitter path of the switching transistor 78. The resulting conduction of the latters collector path therefore grounds line 42, thereby energizing or turning on the oscillator 22. It should be understood that the oscillator will continue to operate so long as a positive voltage is applied at point 52 of the transformer 48 and transistor 78 is conducting and that the operation of the oscillator will terminate if transistor 78 is shut off, even though positive voltage continues to be applied to point 52 of transformer 48.

In accordance with an important aspect of the present invention, provision is made for automatically terminating the operation of the oscillator in the event ignition of the burner 14 is unsuccessful. For this purpose lenghth of the time period in which ignition can be attempted is measured off by a timing circuit and is largely determined by the period required to charge the capacitor 84 through the emitter-base path of the transistor 76. Normally, one would create the timing action by simply connecting a capacitor in series with a resistance, and utilize a switching device to be turned on for a predetermined desired time while a voltage drop exists across the capacitor. But to obtain a relatively long time period, relatively large values of resistance and capacitance would be required to provide a large time constant (RxC). In the present case, however, small values of resistance and capacitance result in a long measured time period because the gain of transistor 76 is, in effect, multiplied bythe time constant that would be obtained in a normal series circuit because the capacitor 84 is in the emitter-base circuit, and the switching device 78 is in the collector circuitof the transistor 76. Since the base current is defined as the ratio of the collector current to the gain of the transistor 76, only a small fraction of the emitter current can flow to charge the capacitor 84. Therefore, the effective time constant is approximately equal to the product of the transistor gain and the normal RC time constant (the latter being the product of the resistance R of 72, 18a and the base-emitter junction of 78 times the capacitance of the capacitor 84). Thus, when thermostat switch 28 closes and voltage from source 24 is thereby applied to the diodes 72 and 50, current flows through the coil 18a and the emitter-base path of transistor 76 to start charging of the capacitor 84; and the resulting collector current through transistor 76 turns on transistor 78 to energize the oscillator. As this begins, the capacitor 84 charges at a relatively slow rate because of the small magnitude of the emitter-base current through resistor 76, and thus it may require a relatively long period for the voltage on the capacitor to rise sufficiently to reduce that current to a low value which cuts off the collector current. With only a relatively small capacitor 84, and relatively small total resistance in the emitter-base path of the common base amplifying transistor 76, the actual timing period may be made relatively long because the actual time constant RxC is, in effect, multiplied by the gain of the transistor. Unless a predetermined response is received within the time required for the capacitor to approach full charge, the emitter-base current will decay sufficiently to cut off transistor76, thereby turning off transistor 78 and terminating the operation of the oscillator to cause the sparking to cease. More importantly, when the transistor 76 is cut off after a predetermined time, excitation current through the coil 18a ceases (as explained below), and the valve 18 closes to prevent accumulation of an explosive quantity of fuel near the burner 14. When capacitor 84 is fully charged and the switch 26 and thermostat 28 remain closed, transistor 76 and 78 (as well as valve 18) remain shut off and the timing circuit is in a lockout mode so long as capacitor 84. remains charged.

The user may then open either the switch 28 or thermostat 28 to permit the capacitor 84 to gradually discharge through resistor 86, thereby resetting the timing circuit. Reclosure of the previously opened switch will cause repetition of the foregoing sequences to again attempt ignition at the burner. It is preferred that the values of the components (i.e., capacitor 84, resistance of coil 18a, transistor 76) be selected so that initial ignition trial be within the range of about 5 to about seconds, so that an unsuccessful ignition within the predetermined time or trial period will cause lockout.

In accordance with another aspect of the present invention, the operation of the oscillator is automatically terminated if ignition of the burner 14 is successful. This is achieved by providing a shunting circuit bypassing transistor 76 and permitting current to continue to flow through the coil 18a. This is effective to keep the solenoid valve 18 open while shutting off the transistors 76 and, 78 as well as the oscillator 22. The shunting circuit comprises a transistor 90 having its emitter connected between the coil 18a and the emitter of the transistor 76, with its base being connected to ground through a heat sensitive or photo-sensitive device, here a photo-resistor 92, which is positioned adjacent the burner 14 in a manner such that it views or monitors the presence of a flame in the burner. If the ignition attempt is successful, the resistance of the photo-resistor will drop from its dark resistance value of several megohms to a substantially lower resistance value, preferably approximately 10,000 ohms. This allows a flow of base current sufficient to saturate transistor 90, so that its collector passes the excitation current through the coil 18a. When the shunting circuit is operating, the emitter of transistor 76 is pulled down essentially to ground potential, so that only negligible current can flow through either the emitter or base. The capacitor 84 will dissipate its charge through resistor 86 so that if the flame is lost, the photo-resistor 92 will return to its high resistance value, shutting off transistor 90. In such event, and assuming that thermostat 28 has not been opened because of the heating action from the burner 14, voltage will be reapplied to turn on transistors 76 and 78 and allow the oscillator to again operate to initiate sparking in an automatic attempt for reignition. As previously described, transistor 76 will only conduct for the time required to recharge capacitor 84 to a value such that transistor 76 is cut off. It is within the scope of the invention, as thus far described, to choose the valve 18, coil 18a and source voltage 24 such that the valve 18 is opened at all times when the transistor 76 is conducting and the switch.

transistor 78 is turned on to enable the oscillator 22. In such an arrangement, the valve 18 would open when the transistor 76 turns on in response to closure of thermostat 28 (and even though the transistor 78 or the oscillator 22 failed to operate properly), and would reclose if the burner fails to ignite when the capacitor 84 charged enough to reduce the emitter-base current of transistor 76 such that its collector current drops below the holding current level for coil 18a. In keeping with another aspect of the invention, however, provision is made to preclude actuation of the valve l8 unless and until the enabling device is operating as a virtual certainty, i.e., until sparking at gap l0, 12 is almost certainly occurring to enable the result (flame ignition) intended when the valve 18 is actuated. In the present instance, the enabling device is comprised of the transistor 78, the oscillator 22 and the spark generator 20 since sparking will not occur unless all of these components are functioning properly.

This desirable safety function is achieved by feedback which permits the valve 18 to be actuated when the enabling device is in fact actuated and working. For this purpose, the coil 18a is sized such that application of approximately the voltage (here, 6 volts) from the source 24 will produce holding current to maintain the valve 18 actuated, but not current sufficiently great to pick up or initially actuate the valve 18. Although two separate windings may be associated with the valve 18, with pickup occurring only when both are excited and holding occurring when only one is excited, the embodiment here shown requires but a single valve coil 18a which is sized such that the valve will hold open if approximately 4.5 volts is applied across that coil but such that initial pickup of the valve will transpire only if an appreciably greater voltage (e.g., about 8 volts) is applied to the coil. Although the amount of additional voltage required to initially actuate the valve is not critical, it is preferred that the required coil pickup voltage be approximately at least percent higher than the voltage of the source 24, but that coil holding voltage be less than its initial energization value, so that the voltage source 24 is sufficient to hold it open. In addition to the above safety feature, this two-level voltage operation of the solenoid valve also has the advantage of reducing power drain from the source 24 after it has been initially opened or energized.

To supply the additional voltage required to initially actuate the valve 18, another secondary winding 96 is provided in the transformer 48 which is connected through a diode 98 to a capacitor 100. Whenever the oscillator 22 is operating, the ac. voltage in the winding 98 is rectified to produce a dc. voltage of the polarity indicated acrossthe capacitor 100, this being limited by a parallel Zener diode 110 but being substantially greater than the voltage supplied by the battery 24. The voltage across the capacitor 100 (say about 10 volts) is coupled via a conductor 103 to the upper end of coil 18a and thus so long as the oscillator is operatingthe supplemental or higher voltage drives current through thecoil and transistor 76 to ground, the larger current being sufficient to pick up or actuate the valve 18. The higher voltage from capacitor 100 reversely biases the diode 72 and thus shuts off current flow from source 24 through the coil 18a while the oscillator is operating. Since this voltage provides a source of positive feedback to the oscillator, it would be difficult to shut off the oscillator if the voltage became too high and, accordingly, the Zener diode 110 is provided to clamp the voltage to the level of about 10 volts. The desirable feature of the described safety circuit is that the solenoid valve 18 cannot be initially actuated from the voltage of the source 24 alone. The higher voltage across the capacitor 100 will not be present -because the oscillator 22 will not be operating if the transistor 78 is defective, or if the oscillator itself is defective. Thus, the solenoid valve cannot be initially actuated unless the associated combustion enabling-device, i.e., the oscillator 22 and sparking circuit 20, are operating to charge the capacitor 100. Noteworthy is the fact that while the oscillator is operating the capacitor 84 will charge to a voltage greater than that of the source 24 before the timing circuit times out. If ignition has not occurred by this time to create a-shunt path through the transistor 90, the valve coil 18a is abruptly deenergized to close the valve 18. This is so because stoppage of the oscillator and discharge of the capacitor 100 leaves the voltage on the capacitor 84 sufficiently high to reverse bias the base-emitter junction of the transistor 76, cutting off its collector current.

In summary, when the thermostat 28 closes to call for heat, the timing circuit formed by transistor 76 and capacitor 84 control the switching device 78 so that the oscillator 22 is turned on to produce sparking at the gap 10, 12. If the oscillator operates correctly (thereby assuring sparking) the supplemental voltage from capacitor 100 causes opening of the fuel valve. If fuel ignition at the burner for any reason fails to occur in the predetermined period measured off by the charging of capacitor 84, the timing circuit locks out and shuts off the oscillator, thereby reclosing the valve 18. But if a flame appears at the burner within the predetermined period, the photo-resistor 92 makes transistor 90 conductive to maintain holding current through the coil 18a'and the valve 18 stays open. When the predetermined period ends, transistor 76 is turned off and this shuts off oscillator 22. And when thermostat 28 becomes satisfied andreopens, the coil 18a is deenergized to reclose the fuel valve 18.

Turning now to a modification also embodying the present invention and shown in FIG. 2, a schematic circuit diagram is illustrated which has the capability of independently controlling two burner devices, such as may be required for a camping trailer or self propelled camper or the like that may have more than one appliance with a fuel burner. For example, a burner in a space heating unit as well as a water heater may be independently controlled. A significant advantage of the schematic circuitry illustrated in FIG. 2 is that a single power source 24, main switch 26, oscillator 22 and sparking circuit 20 may be utilized in controlling two separate burners completely independently of one another to thereby reduce the cost of the circuitry over what would be required if two embodiments of the invention as shown in FIG. 1 were utilized. However, the sparking circuit 20 reqquires a slight alteration in that the transformer 64 has an additional secondary winding 67 which is required to produce sparks or arcing between electrodes 10 and 12 that are positioned adjacent the additional burner 14.

In keeping with the present invention, timing, safety and monitoring circuits are provided for independently controlling each of the burners 14 and 14', with the thermostat 28 operating with respect to the burner 14 and a separate thermostat 28' operating with respect to the burner 14'. Assuming that the burner 14 is a part of a water heater, for example, wherein it is desired to keep the temperature of the water within a predetermined range, the thermostat 28 may comprise two series connected switches 120 and 122, with the switch 120 being normally open and adapted to automatically close when the water temperature falls below the desired minimum temperature. Similarly switch 122 is shown normally closed and opens if the water temperature exceeds the desired maximum temperature. The combination of the two switches 120 and 122 are thereby operable to maintain the temperature within a desired range.

Thus, in operation, if the main switch 26 is closed, the circuitry associated with each of the burners l4 and 14' would be operable, and assuming the water temperature of the water heater incorporating the burner 14 is below the minimum level, switch 120 would close and apply voltage from the source 24 to a diode 72', the cathode of which is connected through the solenoid coil 18a to the emitter of the amplifying semiconductor device, which is also shown to be a transistor 76.

The collector of transistor 76 is connected through a diode 80 to the base of a switching device, which is shown to be a transistor 78'. Additionally, the base of the transistor 76 is connected through a diode 82 to a parallel connected capacitor 84' and resistor 86' which lead to ground. The switching transistor 78 has its collector connected to the line 42 of the oscillator 22 and its emitter connected to ground so that when the positive source voltage is applied through the diode 50' to the transformer 48, current also flows through the diode 72', coil 18a, emitter and base of transistor 76, a diode 82 and into a capacitor 84' to charge the latter. Such emitter-base current turns on current flow through the emitter-collector path of the transistor 76' and this current turns on the switching transistor 78' which thus grounds line 42 thereby energizing or turning on the oscillator 22.

In keeping with the invention, it will be understood from the foregoing that either the circuitry associated with the burner 14 previously described or the circuitry associatedwith burner 14' is effective to turn on the oscillator 22 and the oscillator will continue to operate so long as a positive voltage is applied at pooint 52 of the transformer 48 and either of the transistors 78 or 78' is conducting, and that the operation of the oscillator will terminate if both transistor 78, 78 are shut off even though positive voltage continues to be applied to point 52 of the transformer 48. As in the case with respect to the operation of the circuitry associated with the burner 14, the circuitry associated with the burner 14' will automatically terminate the operation of the oscillator in the event ignition of the burner 14 is unsuccessful. As current flows through the coil 18a and transistor 76' to turn on transistor 78 and energize the oscillator 22, the capacitor 84 starts charging but at a slow rate because of the small magnitude of the emitter-base current through the transistor 76'. Unless a predetermined response is received within the time required for the capacitor to approach full charge, the emitter-base current will decay sufficiently to cut off transistor 76' and thereby turn off transistor 78 and terminate the operation of the oscillator to cause sparking at the electrode gap 10, 12 to cease. When capacitor 84' is fully charged and the switch 26 and thermostat 28 remain closed, transistors 76' and 78' as well as valve 18' remain shut off and the timing circuit is in a lockout mode. If either the switch26 or thermostat 28 is opened, the capacitor 84' will gradually discharge through resistor 86' and thereby reset the timing circuit. Reclosure of the previously opened switch will cause repetition of the foregoing sequence to again attempt ignition at the burner 14.

The operation of the oscillator is automatically terminated if ignition of the burner 14' is successful and the circuitry associated with the burner 14 is not operative to energize the oscillator. This is achieved substantially as described with respect to the embodiment as illustrated in FIG. 1 by providing a similar shunting circuit bypassing the transistor 76' and permitting current to continue to flow through the coil 18a. This is effective to keep the solenoid valve 18 open while shutting off the transistors 76 and 78. The shunting circuit comprises a transistor 90' having its emitter connected to the coil 18a and the emitter of the transistor 76, with its base being connected to ground through a heat sensitive or photo-sensitive device, here a photo-resistor 92, which is positioned adjacent the burner 14' in a manner such that it also views or monitors the presence of a flame in the burner 14'. If the ignition attempt is successful, the resistance of the photo-resistor will drop from its dark resistance value of several megohms to a substantially lower resistance value, which is preferably also approximately 10,000 ohms. This allows flow of base current sufficient to saturate a transistor 90' so that its collector passes the excitation current through the coil 18a. Thus, when the shunting circuit is operating, the emitter transistor 76' is pulled down essentially to ground potential, so that only negligible current can flow through either the emitter or the base of transistor 76'. The capacitor 84 will dissipate its charge through resistor 86' so that if the flame is lost, the photo-resistor 92' will return to its high resistance value, shutting off transistor In such event, voltage will be reapplied to turn on transistors76' and 78 and allow the oscillator 22 to again operate to initiate sparking in an automatic attempt for re-ignition.

To prohibit the solenoid valve 18' from being energized when, due to some circuit failure, sparking is not taking place at the gap 10', 12, the solenoid coil 18a is also preferably sized to require voltage that exceeds voltage of the power source 24 to initially open the valve. To supply the higher required voltage, the secondary winding 96 provided in the transformer 48 which, as previously described, is connected through the diode 98 to the capacitor 100.

In the arrangement of FIG. 2, however, mutual isolation circuits are provided to prevent starting of the timing circuit 76, 84 and energization of the coil 180 when the thermostat 28 closes; and conversely to prevent starting of the timing circuit 76', 84' and energization of the coil 18a when the thermostat 28 closes. As here shown, the line 103 is coupled to the two coils 18a and 18a through respective transistor switches 102 and 102' which are enabled only if the thermostat 28 or 28 is respectively closed. If thermostat 28 only is closed, then the source voltage is applied to a voltage divider 106, 107 which produces base-emitter current in a transistor 104. Collector current through the latter results in emitter-base current in transistor 102, which is thus turned on to couple the +10 volts from line 103 to the upper end of coil 18a so that valve 18 is picked up. But because thermostat 28' is open, the voltage from source 24 is not applied to the correspondingvoltage divider 106', 107' and the transistors 102 and 104 remain non-conductive to preclude energization of the coil 18a and actuation of the valve 18'. The same sort of isolation of the coil 18a from the: high voltage on the capacitor takes place when the thermostat 28' alone closes, in which case the transistors 102and 102 are respectively conductive and non-conductive. In either case, the fuel valve 18 or 18' corresponding to the closed thermostat can be actuated only if the oscillator 22 is operating and sparks are occurring in the two gaps 10, 12 and 10, 12'. Thus, a common voltage source 24 and single oscillator 22 in FIG. 2 serve two separate burners while each burner is independently controlled by its own timing circuit and thermostat.

It should be understood from the foregoing that although the circuitry associated with either the burners 14 or 14' may activate the oscillator 22, the burners 14 and 14 are, in fact, independently controlled, since the absence of energization of one of the solenoid valves will prevent ignition of its corresponding burner since fuel will not be transmitted to that burner, even though the oscillator and sparking circuits are operating in an attempt to ignite the other burner.

Thus, a system for controlling a utilization device has been described in the environment of a fuel burner ignition system which has the advantages of low power consumption during operation, automatic control of the operation of the burners as well as numerous safety features.

I claim as my invention:

1. In a control system for actuating an enabling device and a utilizatiion device, the combination comprising a. means including an on-off switch for connecting a utilization device in a first series circuit across a dc.

voltage source, the source votlage and the resistance of the first series circuit being related in magnitude such that exciting current flows which is insufficient to actuate said utilization device,

b. means responsive to current flow through said series circuit for turning on an enabling device to actuate the same,

c. means responsive to operation of said enabling device for producing a supplemental dc. voltage greater in magnitude than said source voltage, and

d. means for applying said supplemental voltage across said utilization device to produce an increase in current flow therethrough sufficient to actuate said utilization device,

' whereby said utilization device is actuated in response to completion of said first series circuit only if said enabling device is operatively activated.

2. In a control system as defined in claim 1 including means responsive to a condition which results only from simultaneous actuation of the utilization and enabling devices, for turning off said enabling device while maintaining said utilization device actuated responsive to receiving a predetermined response within a predetermined time.

3. In a control system as defined in claim 1 wherein said enabling device comprises a dc. to ac. converter and means connected to said converter for generating sparks at a gap when said converter is active.

4. In a system for supplying electrical energy to an auxiliary device and turning on a utilization device only if the electrical supplying means is operating, the combination comprising a. a utilization device having an actuating coil,

b. means for selectively connecting said coil in a series circuit across a dc. voltage source,

bl. the resistance of said series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the series circuit, the coil current is not sufficient to actuate said utilization device,

c. a dc. to ac. converter having an input circuit and having an output transformer coupled to supply energy to said auxiliary device,

(1. means responsive to current flow in said series circuit for connecting said converter input circuit across said dc. voltage source, whereby the converter is normally effective to transmit energy to said auxiliary device,

e. means for rectifying an ac. ouptut voltage from said transformer to produce a supplementary dc. voltage greater in magnitude than said source voltage, and

f.- means for applying said supplemental output voltage to the series circuit which includes said coil, said supplementary voltage being in magnitude sufficient to cause current flow through the coil to actuate said utilization device, whereby said utilization device is actuated substantially only under conditions such that said converter is operative and the auxiliary device is receiving electrical energy.

5. In a system as defined in claim 4 wherein said auxiliary device comprises means for producing sparkss in a gap between two electrodes.

6. In a system as defined in claim 5 wherein said utilization device is a solenoid valve interposed in the fuel line of a burner, said electrodes being positioned adjacent said burner so that said sparks are adapted toignite fuel, in the event said solenoid valve is actuated to transmit fuel to the burner.

7. In a control system for turning on a utilization device and an enabling device, dropping out the enabling device if a predetermined response is produced within a predetermined time, but dropping out both devices if such response is not received within said time, the combination comprising a. an amplifying semiconductor device having emitter-base and emitter-collector current paths;

b. a capacitor;

c. means for connecting the utilization device, the emitter-base path, and the capacitor in series across a source voltage;

d. means for connecting the utilization device and the emitter-collector path in a series circuit across said source voltage;

e. an enabling device and means responsive to current flow in said series circuit for turning on said enabling device; and,

f. means responsive to a condition which can result only from simultaneous actuation of the utilization and enabling devices for shunting said emitter-base path, thereby to turn off said enabling device while continuing actuating current flow through the utilization device;

whereby substantially full charging of said capacitor to the source voltage before occurrence of said condition results in termination of current in said emitter-base path and de-actuation of both the utilization and enabling device.

8. A control system as defined in claim 7 wherein said shunting means comprises a normally high resistance path connected across said emitter-base path and capacitor, said shunting means changing to low resistance responsive to said condition.

9. A control system as defined in claim 8 wherein said shunting means includes a photo-sensitive device having a normally high dark resistance value and a lower resistance value when energized by the presence of light, said condition being the existence of a light emitting flame in a burner.

10. A control system as defined in claim 7 wherein a resistor is connected in parallel with said capacitor to enable discharging thereof so that said utilization device is adapted to be re-actuated after the capacitor discharges.

ll. A control system as defined in claim 10 wherein said utilization device is a solenoid valve interposed in a fuel line for an appliance.

12. In a system for supplying fuel to a burner only if an ignition spark gap is excited to ignite the fuel, the combination comprising a. a solenoid valve adapted to be interposed in a conduit leading from a combustible fuel source to a burner, said valve having a coil which actuates and opens the valve when a current of greater than a predetermined magnitude flows therethrough.

b. means for selectively connecting said coil in a series circuit across a dc. voltage source,

b1. the resistance of said series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the series circuit, the coil current is not greater than said predetermined magnitude,

c. a dc. -to-ac. converter having input terminals and having an output transformer with output terminals,

(1. means coupling said output terminals to said spark gap to transfer energy from said converter to said gap to create gap sparking when said converter'is active,

e. means responsive to current greater or less than said predetermined magnitude in said series circuit connecting said input terminals across said dc. voltage source to activate said converter,

f. an auxiliary output winding associated with said transformer and having an ac. voltage induced therein when said converter is active,

g. means for rectifying the ac. voltage induced in said auxiliary winding to produce a supplemental dc. voltage when said converter is active, said supplemental voltage being greater than the dc. source voltage, and

h. means for applying said supplemental dc. voltage to the said series circuit which includes said coil, thereby to cause coil current greater than said predetermined magnitude.

whereby said valve is actuated to supply fuel to the burner substantially only under conditions such that ignition sparking is occurring at the spark gap.

13. In a system as defined in claim 12 wherein a second fuel burner is controlled, a second spark gap being positioned adjacent said second burner, the combinatiion including a second solenoid valve interposed in a conduit leading from a combustible fuel source to said second burner, said second valve having a coil which actuates and opens the valve when a current of greater than a predetermined magnitude flows therethrough,

second means for selectively connecting said second valve coil in a second series circuit across said dc. voltage source, the resistanceof said second series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the second series circuit, the second valve coil current is not greater than said predetermined magnitude,

means coupling said output terminals to said second spark gap to transfer energy from said converter to said gaps to create sparking in said gaps when said converter is active,

means responsive to current greater or less than said predetermined magnitude in said second series circuit for connecting said input terminals across said dc. voltage source to activate said converter,

means for applying said supplemental dc. voltage to said second series circuit which includes said second valve coil, thereby to cause second valve coil current greater than said predetermined magnitude,

whereby said second valve is actuated to supply fuel to the second burner substantially only under conditions such that ignition sparking is occurring at the second spark gap. 

1. In a control system for actuating an enabling device and a utilizatiion device, the combination comprising a. means including an on-off switch for connecting a utilization device in a first series circuit across a dc. voltage source, the source votlage and the resistance of the first series circuit being related in magnitude such that exciting current flows which is insufficient to actuate said utilization device, b. means responsive to current flow through said series circuit for turning on an enabling device to actuate the same, c. means responsive to operation of said enabling device for producing a supplemental dc. voltage greater in magnitude than said source voltage, and d. means for applying said supplemental voltage across said utilization device to produce an increase in current flow therethrough sufficient to actuate said utilization device, whereby said utilization device is actuated in response to completion of said first series circuit only if said enabling device is operatively activated.
 2. In a control system as defined in claim 1 including means responsive to a condition which results only from simultaneous actuation of the utilization and enabling devices, for turning off said enabling device while maintaining said utilization device actuated responsive to receiving a predetermined response within a predetermined time.
 3. In a control system as defined in claim 1 wherein said enabling device comprises a dc. to ac. converter and means connected to said converter for generating sparks at a gap when said converter is active.
 4. In a system for supplying electrical energy to an auxiliary device and turning on a utilization device only if the electrical supplying means is operating, the combination comprising a. a utilization device having an actuating coil, b. means for selectively connecting said coil in a series circuit across a dc. voltage source, b1. the resistance of said series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the series circuit, the coil current is not sufficient to actuate said utilization device, c. a dc. to ac. converter having an input circuit and having an output transformer coupled to supply energy to said auxiliary device, d. means responsive to current flow in said series circuit for connecting said converter input circuit across said dc. voltage source, whereby the converter is normally effective to transmit energy to said auxiliary device, e. means for rectifying an ac. ouptut voltage from said transformer to produce a supplementary dc. voltage greater in magnitude than said source voltage, and f. means for applying said supplemental output voltage to the series circuit which includes said coil, said supplementary voltage being in magnitude sufficient to cause current flow through the coil to actuate said utilization device, whereby said utilization device is actuated substantially only under conditiOns such that said converter is operative and the auxiliary device is receiving electrical energy.
 5. In a system as defined in claim 4 wherein said auxiliary device comprises means for producing sparkss in a gap between two electrodes.
 6. In a system as defined in claim 5 wherein said utilization device is a solenoid valve interposed in the fuel line of a burner, said electrodes being positioned adjacent said burner so that said sparks are adapted to ignite fuel, in the event said solenoid valve is actuated to transmit fuel to the burner.
 7. In a control system for turning on a utilization device and an enabling device, dropping out the enabling device if a predetermined response is produced within a predetermined time, but dropping out both devices if such response is not received within said time, the combination comprising a. an amplifying semiconductor device having emitter-base and emitter-collector current paths; b. a capacitor; c. means for connecting the utilization device, the emitter-base path, and the capacitor in series across a source voltage; d. means for connecting the utilization device and the emitter-collector path in a series circuit across said source voltage; e. an enabling device and means responsive to current flow in said series circuit for turning on said enabling device; and, f. means responsive to a condition which can result only from simultaneous actuation of the utilization and enabling devices for shunting said emitter-base path, thereby to turn off said enabling device while continuing actuating current flow through the utilization device; whereby substantially full charging of said capacitor to the source voltage before occurrence of said condition results in termination of current in said emitter-base path and de-actuation of both the utilization and enabling device.
 8. A control system as defined in claim 7 wherein said shunting means comprises a normally high resistance path connected across said emitter-base path and capacitor, said shunting means changing to low resistance responsive to said condition.
 9. A control system as defined in claim 8 wherein said shunting means includes a photo-sensitive device having a normally high dark resistance value and a lower resistance value when energized by the presence of light, said condition being the existence of a light emitting flame in a burner.
 10. A control system as defined in claim 7 wherein a resistor is connected in parallel with said capacitor to enable discharging thereof so that said utilization device is adapted to be re-actuated after the capacitor discharges.
 11. A control system as defined in claim 10 wherein said utilization device is a solenoid valve interposed in a fuel line for an appliance.
 12. In a system for supplying fuel to a burner only if an ignition spark gap is excited to ignite the fuel, the combination comprising a. a solenoid valve adapted to be interposed in a conduit leading from a combustible fuel source to a burner, said valve having a coil which actuates and opens the valve when a current of greater than a predetermined magnitude flows therethrough. b. means for selectively connecting said coil in a series circuit across a dc. voltage source, b1. the resistance of said series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the series circuit, the coil current is not greater than said predetermined magnitude, c. a dc. -to-ac. converter having input terminals and having an output transformer with output terminals, d. means coupling said output terminals to said spark gap to transfer energy from said converter to said gap to create gap sparking when said converter is active, e. means responsive to current greater or less than said predetermined magnitude in said series circuit connecting said input terminals across said dc. voltage source to activate said converter, f. an auxiliary output winding associated with said trAnsformer and having an ac. voltage induced therein when said converter is active, g. means for rectifying the ac. voltage induced in said auxiliary winding to produce a supplemental dc. voltage when said converter is active, said supplemental voltage being greater than the dc. source voltage, and h. means for applying said supplemental dc. voltage to the said series circuit which includes said coil, thereby to cause coil current greater than said predetermined magnitude. whereby said valve is actuated to supply fuel to the burner substantially only under conditions such that ignition sparking is occurring at the spark gap.
 13. In a system as defined in claim 12 wherein a second fuel burner is controlled, a second spark gap being positioned adjacent said second burner, the combinatiion including a second solenoid valve interposed in a conduit leading from a combustible fuel source to said second burner, said second valve having a coil which actuates and opens the valve when a current of greater than a predetermined magnitude flows therethrough, second means for selectively connecting said second valve coil in a second series circuit across said dc. voltage source, the resistance of said second series circuit being in magnitude relative to the dc. source voltage such that, upon completion of the second series circuit, the second valve coil current is not greater than said predetermined magnitude, means coupling said output terminals to said second spark gap to transfer energy from said converter to said gaps to create sparking in said gaps when said converter is active, means responsive to current greater or less than said predetermined magnitude in said second series circuit for connecting said input terminals across said dc. voltage source to activate said converter, means for applying said supplemental dc. voltage to said second series circuit which includes said second valve coil, thereby to cause second valve coil current greater than said predetermined magnitude, whereby said second valve is actuated to supply fuel to the second burner substantially only under conditions such that ignition sparking is occurring at the second spark gap. 